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The 2D HSQC (Heteronuclear Single-Quantum Correlation) experiment permits to obtain a 2D heteronuclear chemical shift correlation map between directly-bonded 1H and X-heteronuclei (commonly, 13C and 15N) . It is widely used because it is based on proton-detection, offering high sensitivity when compared with the conventional carbon-detected 2D HETCOR experiment. Similar results are obtained using the 2D HMQC experiment.

Easy implementation on any AVANCE spectrometer equipped with an inverse probehead
The basic 2D HSQC pulse sequence consists of four independent parts ( 80CPL185 and 86JMR546-69 ):
  1. An initial INEPT pulse train transfers polarization from 1H to X via 1J(XH) (see INEPT block).
  2. The antiphase 13C magnetization evolves during the variable evolution t1 period under the effect of X chemical shift. Heteronuclear 1H-X couplings are refocused by applying a 180º 1H pulse at the middle of this period (see 1H-decoupled X evolution block).
  3. A retro-INEPT pulse train converts X magnetization to in-phase 1H magnetization (see reverse-INEPT block).
  4.  Proton acquisition is performed with X decoupling (see 1H-acquisition with X-decoupling).
The 2D HSQC experiment can be recorded in routine/automation modes. Minor changes are required if a predefined parameter set is available.The interpulse d2 delay is optimized to 1/2*JCH (3.3-3.8 ms).
More details on practical implementation of ge-2D HSQC experiments on AVANCE spectrometers can be found in the corresponding tutorials:
The HSQC spectrum correlates chemical shifts of heteronucleus X (F1 dimension) and protons (F2 dimension) via the direct heteronuclear coupling 1J(XH). Carbon decoupling is usually performed during proton acquisition and the corresponding satellites colapse to a single resonance showing all proton-proton couplings.
Comparison of different 2D inverse correlations have been carried out ( 90JMR304-86 and 90JMR488-87 ).

Related sequences: